Slurry for chemical mechanical polishing of cobalt

ABSTRACT

A slurry for chemical mechanical polishing of Co. The slurry comprises components by weight as follows, Inhibitor 0.01-2%, Oxidant 0-5%, Abrasive 0.1-10%, Complexing agent 0.001-10%, and the rest of water. The pH value of the slurries is adjusted to 3-5 by a pH value adjustor. The inhibitor is chosen from one or more kinds of five-membered heterocycle compound containing S and N atoms or containing S or N atom. The oxidant is one or more chosen from H 2 O 2 , (NH 4 ) 2 S 2 O 8 , KIO 4 , and KClO 5 . The abrasive is one or more chosen from SiO 2 , CeO 2 , and Al 2 O 3 . The complexing agent is one or more chosen from amino acid and citric acid. The slurry can effectively prevent Co over corrosion and reduce the polishing rate of Co in the polishing process.

TECHNICAL FIELD

The present invention relates to microelectronics technology, especiallyrelates to chemical mechanical polishing (CMP) slurries and relatedapplications.

BACKGROUND OF THE INVENTION

With the continuous shrink of feature size in ultra large scaleintegrated Circuits (ULSI) technology, the size of the copperinterconnect structure is getting more and more smaller. To reduce theRC delay, the thickness of barrier or adhesion layer in the copperinterconnect structure is getting thinner. The traditional copperbarrier/adhesion layer stack—Ta/TaN is not suitable any more, as theresistivity of Ta is relatively high and copper cannot be directlyelectroplated onto Ta. Compared with Ta, cobalt has lower resistivityand is relatively cheaper. The adhesion between Cu and Co is good. Cucan easily nucleate on Co, also copper can be directly electroplated oncobalt.

Porous low k dielectrics material has been already used in the currentinterconnect structures. It is reported that low k can be easily damagedby plasma or polishing slurries. In current chemical mechanicalpolishing processing, to reduce the damage to low-k dielectrics, most ofthe current slurries used for copper and barriers are acidic. But it isobserved that copper and cobalt easily suffered from dissolution inacidic solution containing oxidant (H₂O₂). This makes the polishing rateof copper and cobalt is so high that it will induce the dishing ofcopper line. The dissolution of the cobalt adhesion layer on thesidewall of the copper interconnect structure can lead to thedelamination of copper lines and cause reliability problem. So addingeffective inhibitors in the acid slurry is very important, which canreduce the polishing rate of Co, and prevent the dissolution of Colayer. along the sidewall of the copper interconnect structure.

DESCRIPTION OF THE INVENTION

The present invention is to provide a kind of slurry used for chemicalmechanical polishing in microelectronics technology. The slurries of thepresent invention can effectively inhibit the cobalt corrosion rate inthe acid slurry, which can prevent the reliability problem caused byover polishing or corrosion.

To achieve the said object, the present invention provides a kind ofslurry for chemical mechanical polishing of cobalt, which comprisescomponents by weight as follows, inhibitor 0.01-2%, oxidant 0-5%,abrasive 0.1-10%, complexing agent 0.001-10%, and the rest of water. ThepH value of the slurries is adjusted to 3-5 by pH value adjustor.

The inhibitor is chosen one or more from the five-membered heterocyclecompound containing S and N atoms or containing S or N atom, and theirderivatives. The role of the inhibitor is to reduce the corrosion rateof Cu and Co in the slurry, which can improve the efficiency ofplanarization, reduce the dishing defects and prevent the dissolution ofadhesion layer along the sidewall of the interconnect structure.

The oxidant is chosen one or more from H₂O₂, (NH₄)₂S₂O₈, KIO₄, KClO₅.The role of oxidant is to oxidize Cu, Co and the barrier metal into thecorresponding metal oxides, hydroxides or ions. Among all the oxidants,the best choice is H₂O₂. The weight proportion of the oxidant in theslurry is in the range of 0-5%, and the best weight proportion is0.5%-5%.

The abrasive is chosen one or more from SiO₂, CeO₂, and Al₂O₃. The roleof abrasive is to remove the metal or metal reaction products whichcontact with abrasive particles through mechanical friction force. Amongall the abrasives, the best choice is colloidal SiO₂. The size of theabrasive particles has influence on the polishing rate and surfaceroughness. In the present invention, the size of the abrasive is in therange of 10-100 nm.

The complexing agent is chosen one or more from amino acid and citricacid. The role of the complexing agent is to react with the metal ionson the metal surface or in the slurry, which reduces the metal particlesin the slurry and prevents the metal ions contamination.

Said slurry for chemical mechanical polishing of cobalt, therein theslurries have the list proportion of components by weight: inhibitor0.01-1%, oxidant 0.5-2%, abrasives 1-5%, complexing agent 0.4%, and therest of water.

Said slurry for chemical mechanical polishing of cobalt, therein theChosen five-membered heterocycle compound as inhibitors has twoheteroatoms in ring. More detailedly speaking, the inhibitor can bechosen one or more from Benzotriazole, 2-mercaptothiazole,2-mercaptobenzothiazole, imidazole, 2-Aminobenzimidazole,2-Mercaptobenzimidazole and 2-Methylbenzimidazole. Among all theinhibitors, the best choice is Benzotriazole and 2-mercaptothiazole.Benzotriazole and 2-mercaptothiazole can effectively prevent thecorrosion of Cu and Co.

Said slurry for chemical mechanical polishing of cobalt, therein thechosen complexing agent can be one or more kinds of amino acid, such asglycine, glutamic, leucine and arginine acid. The complexing agent canalso be other organic acid, such as citric acid. The best choice isglycine as complexing agent.

Said slurry for chemical mechanical polishing of cobalt, therein the pHvalue adjustor is chosen one or more from nitric acid, sulphuric acid,dilute acetic acid, hydrochloric acid, potassium hydroxide, sodiumhydroxide, sodium carbonate and sodium bicarbonate. The best choices arenitric acid and potassium hydroxide.

In the present invention, we also provide the application of theslurries on chemical mechanical polishing of Co technology. Inintegrated circuits, Co is used as adhesion or barrier layer for copperinterconnects, while Co can also be used as nano-crystalline in memorydevice and metal gate in MOSFET. All the use of Co, cobalt alloy andcobalt compounds in the electric circuit, and the process needingpolishing process, are included in the applications of the presentinvention.

The provided slurries in the present invention have the pH value in therange of 3-5. If the pH value of the slurry is too low, especially whenthe pH value is lower than 2, the CMP slurry can cause corrosion on thecopper lines and the polishing equipment. If the pH value is in therange of 6-8, the SiO₂ abrasives are not stable. If the pH value of theslurry is very high, especially when the pH value is higher than 9, theslurries can damage the low-k dielectrics. So in the present invention,the pH values of the slurries are adjusted in the range of 3-5.

The slurries for chemical mechanical polishing of Co in the presentinvention can effectively inhibit Co corrosion rate and reduce thepolishing rate of Co, which can effectively reduce the defects afterpolishing process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 a is the cross-sectional schematic structure of the dualdamascene structure before polishing. FIG. 1 b is the cross-sectionalschematic structure of the dual damascene structure after polishing.

FIG. 2 a is the compared potentiodynamic polarization plots of Co in theslurries(pH=3) in embodiment 1 and contrast 1. FIG. 2 b is the comparedpotentiodynamic polarization plots of Co in the slurries (pH=5) inembodiment 1 and contrast 1.

FIG. 3 is the polishing rate of Co as a function of Benzotriazoleconcentration in the slurries in embodiment 2.

THE BEST METHOD OF APPLYING THE PRESENT INVENTION

Combined with figures and embodiments, the best method of applying thepresent invention is described as following:

The method of applying the slurries in the present invention is similaras the applying of traditional slurries. In the polishing process, waferis held face down by the polishing head on the polishing pad, and theslurries are pumped on the polishing pad and is spread uniformly on thewafer surface with the rotation of polishing platen. The copper andadhesion/barrier layers on the top of the dielectrics are polished awayas the pressure is added between wafer and polishing pad, with therotation of polishing head and platen. It should be noticed that, themethod of applying the slurries described above is based on thetraditional polishing equipments in this field. For the specialpolishing equipment, reasonably adjusting the applying method based onthe real case can also achieve the role of chemical mechanicalplanarization. FIG. 1 a is the cross-sectional schematic structure ofthe dual damascene structure before polishing. FIG. 1 b is thecrosssectional schematic structure of the dual damascene structure afterpolishing by using the slurries in the present invention. In FIG. 1 aand lb, dielectrics 10 could be silicon dioxide, or low-k dielectrics.The materials of copper adhesion/barrier layer 20 could be stackcontaining Co and metal nitrides or metal carbon nitrides, such asCo/TaN, Co/TiN, Co/TaCN, Co/TiCN, or could be a single cobalt alloylayer, such as CoMo, CoTa, CoTi and CoW. The method of depositingadhesion/barrier layer could be Physical vapor deposition (PVD), Atomiclayer deposition (ALD), or chemical vapor deposition(CVD). The materialof etch stop layer 30 could be SiN, SiC, SiCN and other hard etchingdielectrics materials. By using the slurries in the present invention,the excess copper and the adhesion layer and barrier layer 20 abovedielectrics 10 are removed, and the structure shown in FIG. 1 a ischanged into the structure shown in FIG. 1 b. Through the followingembodiments the method of applying the slurries in the present inventionis further described.

EMBODIMENT 1

The components of slurries: 1 wt % colloidal SiO₂; 0.75 wt % glycine;0.12 wt % 2-mercaptothiazole; and the rest of water. Using the dilutednitric acid and potassium hydroxide to adjust the pH value to 3.

The polishing equipment and mechanical parameters: the polisher is CP-4bench top polisher made by CETR Company in this embodiment. Thepolishing pressure is 2 psi, flow rate is 100 ml/min, and rotation rateis 150 rpm for both of polishing head and platen.

Contrast 1

The slurries is the same as those in embodiment 1 except without2-mercaptothiazole; The polishing equipment and mechanical parametersare also the same as those in embodiment 1.

Table 1 lists the corrosion rate and polishing rate of Co in embodiment1 and Contrast 1.

TABLE 1 corrosion rate and polishing rate of Co in embodiment 1 andcontrast 1 2-mercaptothiazole 0 wt % 2- 0.12 wt % mercaptothiazole2-mercaptothiazole Corrosion rate of Co□nm/min□ 5 0 Polishing rate ofCo□nm/min□ 73 27

Shown in table 1, after adding 2-mercaptothiazole in the slurry, thepolishing rate and corrosion rate of Co are obviously reduced. As in thereal interconnect structure, the thickness of the adhesion layer is notgreater than 5 nm, preventing the corrosion of Co is very important. Inembodiment 1, by adding 2-mercaptothiazole in the slurry, the corrosionrate of Co is controlled to a low value and the polishing rate of Co iscontrolled to 27 nm/min. this indicates 2-mercaptothiazole is a goodinhibitor for Co corrosion.

FIG. 2 a is the compared potentiodynamic polarization plots of Co in theslurries(pH=3) in embodiment 1 and contrast 1. FIG. 2 b is the comparedpotentiodynamic polarization plots of Co in the slurries (pH=5) inembodiment 1 and contrast 1. From FIG. 2 a and FIG. 2 b, we can see thatboth of the anodic and cathodic current are reduced obviously no matterthe pH value of slurry is at 3 or 5 after adding 0.12 wt %2-mercaptothiazole, and corrosion current also reduces obviously. Thereis a passivation region on the anodic potentiodynamic polarization plotsof Co in the slurries containing 0.12 wt % 2-mercaptothiazole, and theseindicate 2-mercaptothiazole can adsorb on the surface of Co and thenprevent Co corrosion.

EMBODIMENT 2

The components of slurries: 5 wt % colloidal SiO₂; 0.5 wt % H₂O₂; 0.75wt % glycine; 0-0.24 wt % Benzotriazole; and the rest of water. The pHvalue of the slurry is adjust to 5. The concentrations of Benzotriazoleare controlled to 0.06 wt %, 0.12 wt %, 0.18 wt %, 0.24 wt % for all theslurries.

The polishing equipment and mechanical parameters: the polisher is CP-4bench top polisher made by CETR Company in this embodiment. Thepolishing pressure is 2 psi, flow rate is 100 ml/min, and rotation rateis 150 rpm for both of polishing head and platen.

Table 2 lists the corrosion rate of Co in the slurries with differentconcentrations of Benzotriazole.

TABLE 2 corrosion rate of Co in embodiment 2 Concentrations ofBenzotriazole□wt %□ 0 0.06 0.12 0.18 0.24 Corrosion rate of Co 50 14 9 62 (nm/min)

From the data in table 2, we can see that the corrosion rate of Co isdecreased as the increase of concentration of Benzotriazole. When theconcentration of Benzotriazole is up to 0.24 wt %, the corrosion rate ofCo is reduced to 2 nm/min. This indicates that Benzotriazole is a goodinhibitor for Co corrosion. The mechanism of Benzotriazole inhibiting Cocorrosion could be described as the adsorption of Benzotriazole on Cosurface and then preventing the contact between Co and the slurry,finally preventing the corrosion of Co.

FIG. 3 shows the polishing rate of Co as a function of concentrations ofBenzotriazole in embodiment 2. As it is shown in FIG. 3, the polishingrate of Co is reduced steadily as the increase of Benzotriazoleconcentration. When the Benzotriazole concentration is up to 0.24 wt %,the polishing rate is reduced from 484 nm/min to 75 nm/min. and thecorrosion rate of Co is small (2 nm/min) when Benzotriazoleconcentration is 0.24 wt %. The polishing rate of 75 nm/min is enoughfor polishing the Co or Co alloy adhesion layer with thickness less than5 nm.

EXAMPLE 3-8

The components of the slurries (the rest is water) and the experimentaldata of embodiments 3-8 are listed in table 3.

TABLE 3 components of the slurries and experiment results of embodiments3-8 embodiment 3 embodiment 4 embodiment 5 embodiment 6 embodiment 7embodiment 8 Inhibitor wt % Benzotriazole Benzotriazole/ Benzotriazole/Benzotriazole/ Benzotriazole/ imidazo/ 0.3 % imidazole 2-Aminobenz2-Mercaptob 2-Mercaptoben Benzotriazole/ 1:1) imidazole enzimidazolezimidaz (1.:1) 2-mercaptoth 0.7% (1:1) (1:1) 1.2% iazole (1:1:1) 1% 2%1.8% Oxidant wt % H₂O₂ (NH₄)₂S₂O₈ KIO₄ KClO₄ (NH₄)₂S₂O₈/ H₂O₂/ 0.1%   5%1% 4% H₂O₂ (1.:2) KIO₄ (3:1)   2% 0.6% Abrasive Colloidal Colloidal CeO₂Al₂O₃ Colloidal SiO₂/ Colloidal wt % SiO₂ SiO₂ 3.5%   10%  CeO₂ SiO₂/Al₂O₃/   1% 0.1% (1.:1) Ce02(3:1:1)   7% 5.2% Complexing glycine/citricarginine Citric acid Glutamic acid glycine/ glycine/ agent wt % acid(1.:1) 0.4% 2% 6% Glutamic acid arginine/ 0.1% (3.:1) Citric acid 10%(1.:1:4) 0.8% pH value 3.0 4.0 5.0 4.0 3.0 3.0 Corrosion 1.5 5 3 5 5 2rate of Co □nm/min□ Polishingrate 45 85 100 220 120 60 of Co □nm/min□The proportion is by weight in embodiments 3-8.

The present invention involves a polishing technology using Co or Coalloy as a metal layer in the integrated circuit. In integrated circuit,Co is mainly used as a barrier layer or adhesion layer for coppermetallization, but Co could also be used as nano-crystalline in memorydevises, self-aligned silicide and metal gate for MOSFET. All the use ofCo, cobalt alloy and cobalt compounds in the electric circuits, and theprocesses needing polishing process, are included in the applications ofthe present invention.

Although the content of the present invention has been detailedintroduced by the embodiments above, we should notice that thedescription about the present invention above should not be a limitationfor the present invention. The expert in this filed can change orreplace the present invention after reading the content above. So theprotected range of this invention should be limited by the claims of thepresent invention.

1. A slurry for chemical mechanical polishing of Co, comprisescomponents by weight as follows, inhibitor 0.01-2%, oxidant 0-5%,abrasive 0.1-10%, complexing agent 0.001-10%, and the rest of water; thepH value of the slurry is adjusted to 3-5 by pH value adjustor; saidinhibitor is chosen from one or more kinds of five-membered heterocyclecompound containing S and N atoms or containing S or N atom; saidoxidant is chosen one or more from H₂O₂, (NH₄)₂S₂O₈, KIO₄, KClO₅; saidabrasive is chosen one or more from SiO₂, CeO₂, and Al₂O₃; saidcomplexing agent is chosen one or more from amino acid and citric acid.2. The slurry for chemical mechanical polishing of Co of claim 1,wherein said slurry comprises components by weight as follows, inhibitor0.01-1%, oxidant 0.5-2%, abrasive 1-5%, complexing agent 0.4%, and therest of water.
 3. The slurry for chemical mechanical polishing of Co ofclaim 1 or claim 2, wherein said five-membered heterocycle compoundchosen as inhibitor has two heteroatoms in ring.
 4. The slurry forchemical mechanical polishing of Co of claim 3, wherein said inhibitoris chosen one or more from Benzotriazole, 2-mercaptothiazole,2-mercaptobenzothiazole, imidazole, 2-Aminobenzimidazole,2-Mercaptobenzimidazole and 2-Methylbenzimidazole.
 5. The slurry forchemical mechanical polishing of Co of claim 4, wherein said inhibitoris mixing of Benzotriazole and 2-mercaptothiazole.
 6. The slurry forchemical mechanical polishing of Co of claim 1 or claim 2 or claim 4 orclaim 5, wherein said particle size of the abrasive is in the range of10-100 nm.
 7. The slurry for chemical mechanical polishing of Co ofclaim 1 or claim 2 or claim 4 or claim 5, wherein said complexing agentis chosen one or more from glycine, glutamic, leucine and arginine acid.8. The slurry for chemical mechanical polishing of Co of claim 7,wherein said complexing agent is glycine acid.
 9. The slurry forchemical mechanical polishing of Co of claim 1, the pH value adjustor ischosen one or more from nitric acid, sulphuric acid, dilute acetic acid,hydrochloric acid, potassium hydroxide, sodium hydroxide, sodiumcarbonate and sodium bicarbonate.
 10. The application of the slurry forchemical mechanical polishing of Co according to claim 1 in polishingprocess.